Brain : Alzheimer’s Association

Your brain is your most powerful organ, yet weighs only about three pounds. It has a texture similar to firm jelly.

It has three main parts:

The cerebrum fills up most of your skull. It is involved in remembering, problem solving, thinking, and feeling. It also controls movement.

The cerebellum sits at the back of your head, under the cerebrum. It controls coordination and balance.

The brain stem sits beneath your cerebrum in front of your cerebellum. It connects the brain to the spinal cord and controls automatic functions such as breathing, digestion, heart rate and blood pressure.

Supply lines

Your brain is nourished by one of your body’s richest networks of blood vessels.

With each heartbeat, arteries carry about 20 to 25 percent of your blood to your brain, where billions of cells use about 20 percent of the oxygen and fuel your blood carries.

When you are thinking hard, your brain may use up to 50 percent of the fuel and oxygen.

The real work of your brain goes on in individual cells. An adult brain contains about 100 billion nerve cells, or neurons, with branches that connect at more than 100 trillion points. Scientists call this dense, branching network a “neuron forest.”

Nerve cells connect to one another at synapses. When a charge reaches a synapse, it may trigger release of tiny bursts of chemicals called neurotransmitters. The neurotransmitters travel across the synapse, carrying signals to other cells. Scientists have identified dozens of neurotransmitters.

Alzheimer’s disease disrupts both the way electrical charges travel within cells and the activity of neurotransmitters.

Activity is highest in red areas and then decreases through the other colors of the rainbow from yellow to blue-violet.

Specific activity patterns change throughout life as we meet new people, have new experiences and acquire new skills. The patterns also change when Alzheimer’s disease or a related disorder disrupts nerve cells and their connections to one another.

Alzheimer’s Disease and the Brain

Alzheimer’s disease leads to nerve cell death and tissue loss throughout the brain. Over time, the brain shrinks dramatically, affecting nearly all its functions.

Scientists are not absolutely sure what causes cell death and tissue loss in the Alzheimer’s brain, but plaques and tangles are prime suspects

More about plaques

Plaques form when protein pieces called beta-amyloid (BAY-tuh AM-uh-loyd) clump together. Beta-amyloid comes from a larger protein found in the fatty membrane surrounding nerve cells.

Beta-amyloid is chemically “sticky” and gradually builds up into plaques.

The most damaging form of beta-amyloid may be groups of a few pieces rather than the plaques themselves. The small clumps may block cell-to-cell signaling at synapses. They may also activate immune system cells that trigger inflammation and devour disabled cells.

More about tangles

Tangles destroy a vital cell transport system made of proteins. This electron microscope picture shows a cell with some healthy areas and other areas where tangles are forming.

Nutrients and other essential supplies can no longer move through the cells, which eventually die.

Progression through the brain

Plaques and tangles (shown in the blue-shaded areas) tend to spread through the cortex in a predictable pattern as Alzheimer’s disease progresses.

The rate of progression varies greatly. People with Alzheimer’s live an average of eight years, but some people may survive up to 20 years. The course of the disease depends in part on age at diagnosis and whether a person has other health conditions.

In mild to moderate stages, brain regions important in memory and thinking and planning develop more plaques and tangles than were present in early stages. As a result, individuals develop problems with memory or thinking serious enough to interfere with work or social life. They may also get confused and have trouble handling money, expressing themselves and organizing their thoughts. Many people with Alzheimer’s are first diagnosed in these stages.

As Alzheimer’s progresses, individuals may experience changes in personality and behavior and have trouble recognizing friends and family members.

Severe Alzheimer’s disease

In advanced Alzheimer’s disease, most of the cortex is seriously damaged. The brain shrinks dramatically due to widespread cell death. Individuals lose their ability to communicate, to recognize family and loved ones and to care for themselves.